Initial ranging (IR) is a process of aligning time points at which signals sent by different terminals arrive at a device at a head end in a multiple-access communications system. When a terminal attempts to access a network, the terminal sends an initial ranging signal to the device at the head end. The device at the head end obtains a time point at which the received initial ranging signal arrives at the device at the head end, uses, based on a preset reference-point time point (for example, a start time point of a timeslot allocated to the terminal), a difference between the two time points as a time offset of the terminal, and then sends the time offset to the terminal. The terminal adjusts, based on the time offset, a time point of sending a signal, so as to ensure that time points at which signals sent by all terminals arrive at the device at the head end are aligned, and ensure normal communication of the multiple-access communications system.